Coast Guard Rules and Regulations for recreational boats as set forth in COMDTINST M16752.2 of Sept. 15, 1978 and specifically Title 33, Chapter 1, Parts 181 and 183 require certification labels stating safe loading capacity be affixed to the hull of boats by manufacturers of less than 20 feet in length. With certain exceptions such boats have flotation quantities as set forth in Subparts E, F, and G of Part 183. Most manufacturers attempt to keep their boats safe for the boating public by meeting the minimum flotation requirements as set forth in the Federal Boat Safety Act of 1971 (amended). However, once a boat has been purchased it is subjected to various forms of compression, and point loading of the hull and deck as may be incurred in usual boating activities including loading and unloading the boat, occasionally running it aground, docking it alongside a pier in rough weather, running in heavy seas or other actions which place stresses on the hull.
Current methods of installation of foam flotation materials in boats do not protect the foam materials from degradation in some cases boats have been constructed whereby the installed foam materials provide the necessary rigidity for the hulls and decks. The most common foam used as a flotation material is a rigid closed cell polyurethane foam having a density of 1.3-3 pounds per cubic foot. This foam is fragile and has a tensile strength of approximately 15-96 p.s.i. and a compressive strength, at 10% deflection of 15-60 p.s.i. A rigid foam material undergoing slight deflection can result in cell damage effectively destroying the flotation ability and even a 10% deflection can cause massive damage to the cellular structure. Conventional construction methods are as follows:
(1) Placing loose logs of foam in the hull deck cavity where they are arranged to move and are unprotected from the forces acting on the hull;
(2) Building a fiberglass hull with from 2 to 4 sets of stringers for overall structural support and blowing the foam in liquid form into the areas between the stringers. The foam is applied within 1 to 5 feet of unsupported hull, which can deflect extensively. The foam, being rigid attempts to prevent this deflection and is quickly damaged; or
(3) Constructing a hull and deck structure which is not self-supporting in itself. While still in the original mold, the hull and deck are clamped together and foam in a liquid form is injected into the cavity. The FRP portion of the hull transfers all forces acting on the hull to this foam core thus jeopardizing the cellular integrity of the set foam.
Thus, the present boat construction state of the art which may originally comply with Coast Guard Rules (COMTINST M 16752.2)does little if anything to prevent lowering of the original loading capacity. Also, the methods heretofore used for installing foam flotation materials in boats allows the foam materials to come in contact with water, gas, oil and whatever other substances are commonly found in the hull and deck cavities. When foam, such as rigid polyurethane foam is subjected to sufficient stresses, the cells as heretofore mentioned are damaged or broken and once broken the open cells will absorb and retain fluid in a sponge-like manner. As the cells absorb fluid they resist compression and additional forces to which they may be subjected transfers the forces from the fluid filled damaged cells to adjoining cells causing additional damage or complete destruction. The ability of damaged cellular materials to absorb fluids makes it imperative to protect the cellular structures when employed for flotation purposes and the fact that the damaged cellular materials will not provide the specified flotation properties can be and is a severe current safety problem. Also, as the cellular materials absorb and retain fluid the weight of the boat is increased and in most cases this is unbeknownst to the owner/operator. A severe weight increase can affect the stability and handling properties of the boat and can increase the risk to the occupants. In one known instance the Coast Guard removed a boat of approximately 20 feet in length from service and drained the hull, deck and cavity and found that the boat was approximately 1000 pounds overweight due to fluid absorption which could not be drained from the cellular flotation material.
Absorbed fluids, commonly gasoline and oil can cause severe fire and other hazards. These hazards can be increased as certain designs have their fuel tanks encased in the foam flotation material. It is oftentimes extremely difficult to remove absorbed fluids from the broken cellular materials thus rendering the boat once again safe for its occupants.
With this background in mind the present invention was developed and it is one objective to provide a boat and construction method which will allow the boat to maintain its specified flotation stability and safety characteristics throughout its useful life.
It is still another objective of the present invention to provide a boat hull which will withstand normal impacts without degradation to the cellular flotation members as occurs over the useful life of a boat.
It is yet another objective of the present invention to provide a high strength-to-weight ratio boat hull which can be economically manufactured, and which can be transported at relatively low cost due to its particular stackable features.
It is still another objective of the present invention to provide a boat hull having adequate flotation requirements as set forth in Coast Guard Rules and Regulations in accordance with the Federal Boat Safety Act (as amended), Public Law 92-75 of August 1971.
Another objective of the present invention is to provide a boat which has a hull having a lighter weight per square foot of hull bottom than comparable aluminum boats.
Still another objective of the present invention is to provide a method for boat construction which includes encapsulating cellular flotation logs of specific densities within a boat hull wherein said logs will maintain their cellular integrity throughout the useful life of the boat while undergoing normal stress cycles to the hull.
It is also an objective of the present invention to provide a self-bailing boat construction and method whereby the cellular flotation log members are fully encapsulated to prevent cell degradation by oils or other chemicals and no bridge pump is required to remove water from the hull.
Yet another objective of the present invention is to provide a boat which is stackable in a relative small vertical space requiring no additional side flotation chamber, flotation seats or boxes.
Still another objective of the invention is to provide a boat hull of extremely shallow draft having no interior members to interfere with cleaning or the drainage of water therefrom.
Various other objectives and advantages of the present invention will become obvious to those skilled in the art as the details of the invention are more specifically set forth below.